Thyroid Flashcards
etiologies of hypothyroidism
hashimoto
thyroidectomy
RAI therapy
what drug replaces T4
Levothyroxine
what drug replaces T3
Liothyronine
what was synthroid made from
ground thyroid glands of cows [ew]
are all levothyroxine drugs on the market bio equivalent?
yes
MOA of levothyroxine
active compound= T3–then converted FROM T4 by deiodination in liver & peripheral tissues
how much levothyroxine is absorbed in the small intestine
80%
1/2 life of levothyroxine
7d
how many wks before steady state w/ levothyroxine
4-6wks
where should levothyroxine be stored?
out of heat,light or humidity
how should levothyroxine be taken?
empty stomach before breakfast
or 4hrs after last meal
what is the most important factor with taking levothyroxine
consistancy in timing of dose
dose adjustment when switching PO–> IV
decrease by 50%
how long till SE of levothyroxine go away?
2-3wks
what should we look at if we have a pt on a levothyroxine dose >300
adherence
malabsorption
drug interactions
avg. dose for adult *full replacement
1.6mcg/kg/d
avg. dose for elderly *full replacement
0.5mcg/kg/d
what pt population needs to start levothyroxine on a lower dose?
cardiac pts
how should we dose obese pts on levothyroxine?
w/ their lean body wt dosage
what do we monitor for levothyroxine dose?
TSH
what is 3 situations would warrant TSH checking
new symptoms
drug interaction w/ T4
pregnancy
what pt’s have TSH’s that are misleading
central hypothyroidism d/t hypothalamic or pituitary dz
ADR of levoyhrxoine
palpitation tremor anxiety wt loss tachycardiac increase # poops osteoporosis
what pts are @ risk for cardiac complications (arrythmia, AMI, ACS) on levothyroxine?
cardiac dz
how does levothyroxine cause ACS or dysrhythmia in HF pts
it increase HR and contractility–which increases myocardial O2 demand
what drugs decrease effects of LT4?
amiodarone PTU Antacids Carbamazepine Phenytoin Rifampin
if on levothyroxine when should you take antacids, bile acid resins, fiber, Calcium/iron?
@ a different time b/c it affects absorption
what drugs inhibit T4–>T3 conversion
amiodarone
PTU
what drugs increase LT4 metabolism via cyps
carba
pheny
rifampin
name of pure T3
liothyronine
what has a shorter 1/2 life levo or liothyroine?
liothyronine
when would you prescribe Liotrix?
pts who cannot convert T4–>T3
what is Liotrix made of?
T3 and T4
what is the problem w/ thyroid USP?
levels of T3 and T4 vary ALOT
why do some patients like desiccated thyroid meds?
b/c they get a lift off the fast acting T3, all in their heads (sorry pts)
common causes of hyperthyroidism
graves
multinodular goiter
autonomous nodule
thyroiditis
what are the 3 definitive tx options for hyperthyroidism (not all drugs)
thionamides
RAI
surgery
what is a adjunctive tx options for hyperthyroidism?
b-blockers
Steroids
what are the 2 thionamides we use?
propylthiouracil
Methimazole
MOA of thionamides
inhibit thyroid hormones synthesis by interfering w/ thyroid peroxidase–mediation iodination of tyrosine residues in thyroglobulin
what thionamide do we prefer?
methimazole
why do we like methimazole
Qday
effective @ low dose
major ADR= rare
when do we use PTU
life-threatening thyroid-storm
pregnancy
what happens if methimazole is taken during pregnancy
aplasia cutis
esophageal atresia
how does dosing look for thionamides?
start high–then lower once symptoms are controlled (start lowing 4-8wks in)
how long till partial clinical resolution of thyrotoxicosis?
2 wks
what pts reach remission @ 12-18monthS
small goiter
low levels of anti-TSH ab
mild/mod hyperthyroidsm
fraction of pts on monotherapy of thionamide that reach remission
1/3
what is the recurrent rate of hyperthyroidism
50%
ADR of thionamides
arthralgias
Rash
Gi intolerance
agranulocytosis
what joint problem can develop from thionamide use
anti-thyroid arthritis syndrome
what rheum condition is PTU associated w/
ANCA + vasculitis w/ other symptoms
if a pt on thionamides presents w/ fever, sore throat, mouth ulcers what should you get? why?
CBC w/ diff
agranulocytosis!!!
what can PTU possibly cause in the liver
acute hepatic failure
what do we use for RAI of the thyroid
sodium Iodide I-131
how does Sodium Iodide I-131 work?
thyroid gland takes it up–then it release Beta particles to cause a slow inflammatory response that destroy the thyroid
what should you try prior to RAI
thionamides
main ADR of RAI
radiation thyroiditis–lower neck pain
use of B-blockers in hyperthyroid
decreases symptoms of increased adrenergic tone
once hyperthyoridism resolves what can we do w/ b-blockers
taper down
what steroid do we use in hyperthyroidism
dexamethasone
how does dexamethasone help w/ hyperthyroidism
PREVENTS peripheral conversion of T4–>T3
how does hypothyroidism affect a fetus
increase risk of: miscarriage pre-term birth LBW fetal brain development
what do we need to do to levothyroxine dose in pregnancy
increase (25-30%)
should you take pre-natals and levothyroxine @ the same time of day?
no
can we use desiccated thyroid or lio in pregnancy?
no–not enough T4 gets to fetal brain
when can a pregnant woman resume her levothyroxine dose?
after delivery
what can uncontrolled hyperthyroidism cause in a fetus?
increase risk of: miscarriage gest. HTN pre-term pre-eclamp HF thyroid-storm IUGR premature still born
thionamide used in 1 trimester pregnancy
PTU
thionamide used in 2/3 trimester and breast feeding
methimazole
